Droplet diameters, distribution curves

The influence of wall shear stress on the droplet size distribution for a 4.8-pjn SPG membrane is shown in Figure 16.17 and Figure 16.18. With increasing the wall shear stress from 1.3 to 30 Pa, the droplet size distribution curve shifts to smaller droplet diameters and becomes narrower and narrower. For the given pore size and experimental conditions, an emulsion with a narrow droplet size distribution (span = 0.43) was even produced at a- = 0.37 Pa, corresponding to Vt = 0.3 m/sec and laminar flow inside the membrane tube (Figure 16.13). Williams et al. [49] obtained a span value of 0.82 at the mean tube velocity of Vt = 0.6 m/sec in a semicontinuous... 

Median Diameter. The median droplet diameter is the diameter that divides the spray into two equal portions by number, length, surface area, or volume. Median diameters may be easily determined from cumulative distribution curves. 

Figure 5.12 represents the evolution in time of the surface-averaged droplet diameter for different amounts of solid particles. The kinetic curves confirm the qualitative evolution previously described. The droplet growth is initially rapid but the coalescence rate progressively decreases until the average diameter reaches an asymptotic value. Figure 5.13 shows the change in the droplet size distribution... 

Irnrr and retention time for droplrts to coalesce A pipe diameter is chosen that is large enough to present coalesced 1 droplets from shearing in accordance with the dispersion equation discussed in the previous installment. In effect, the unit grows a droplet distribution curve in the inlet stream that can then be treated in the tank or flume. Fig. 1 shows an ( installation using SP packs in a series of tanks Fig. 2 shows an installation in a series of compartments in a horizontal flume such as a barge bull or a pit. 

In Figure 5 three distribution curves of droplet diameters a-re reported, relative to three axial positions into the furnace. 

The size distribution curve of the droplets in the emulsions varied little if soaps of sodium, potassium, or caesium were used. As a rule the curves had a marked peak, at a diameter of about 2fi, which apparently depended little on the manner of preparation of the emulsion, and slightly on the nature of the oil. Emulsions of water in oil, stabilized by magnesium or aluminium soaps, had a similar distribution of sizes among the droplets. 

The first problem area occurs at a 7 for I2°/6° ratio for weakly absorbing particles where, as exemplified by Figure I, an "S in the characteristic curve precludes a unique determination of a for a measured intensity ratio of 0.5. This results in an uncertainty of about 20% in determined diameter, roughly the same as that from index-of-refraction effects discussed above. In fact, the uniqueness problem adds no new uncertainties since the S phenomenon is covered by the uncertainty band introduced when the absorbing particle intensity ratio curve is assumed to be caused by unknown particle composition. Conversely, this problem must be dealt with when analyzing nonabsorbing particles of a known composition, for instance in a study of cooling tower droplet size distributions. 

There are multiple spray measurements used to quantify an injectors spray quality. Some of these measurements include DIO (arithmetic mean), D32 (Sauter mean diameter), D31 (evaporative mean diameter), DvO.9, and droplet distribution curve. Figure 15.9 provides a description and equation used to calculate SMD, DIO, and D31. Figure 15.10 shows a typical droplet distribution curve with an overlay to show the DvO.9 calculation. The DvO.9 value represents the point where... 

Figure 12 Diameter distribution (cumulative curves) of droplets generated by atomizmg vaned wheel...

Figure 13.6 (a) Volume distributions for the Cumberland power plant (Clarksville, TN) measured at various locations in the plume downwind from the plant on 8/10/79. Secondary aerosol accumulated in all particles up to 1 m—in contrast with the Navajo plant aerosol (Fig. 13.5) which was limited to dp < 0.3 /im. (b) Particle diameter growth rates calculated from data shown in part (a) with a best-fit curve based on an interpolation formula that reduces to the diffusion mechanism for the smaller particles (13,7) and droplet phase reaction for the larger particles (13.8). (After McMurry et al., 1981.)... 

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